Resistance to Sclerotinia sclerotiorum in brassica
and variation in pathogen aggressiveness
John Clarkson and Emma Coventry
Warwick Crop Centre, School of Life Sciences, University of Warwick, Wellesbourne, CV35 9EF, UK
john.clarkson@warwick.ac.uk
Background
Sclerotinia sclerotiorum is an important plant pathogen of oilseed rape (B. napus)
in the UK and worldwide which causes stem rot.
Durable plant resistance to stem rot is very desirable but there are no resistant
oilseed rape cultivars in the UK.
Identifying sources of resistance is challenging as there are many S. sclerotiorum
genotypes which vary in aggressiveness.
Brassica lines with consistent resistance to the most prevalent S. sclerotiorum
genotypes and an understanding of pathogen aggressiveness is required for
successful screening and breeding programmes.
A stem inoculation procedure was developed for brassica
plants (8 true leaves) using wheat grain colonised by S.
sclerotiorum.
18 S. sclerotiorum isolates from different crop hosts and
the wild host meadow buttercup (Ranunculus acris) were
screened against B. napus (oilseed rape cv. Temple), B.
oleracea (broccoli cv. Beaumont) and B. rapa (turnip cv.
Manchester).
10
Number of leaves wilted after 17 days
Variation in pathogen aggressiveness
Isolates from crop hosts
Isolates from buttercup
9
Turnip
Oilseed rape
Broccoli
8
7
6
5
4
3
2
1
0
P2
P7
L17
O92
L6
CE11
C28
L5
L44
R19
HE33
EV9
R30
R28
R12
R17
HE1
DG4
Sclerotinia isolate
Figure 1: Aggressiveness of S. sclerotiorum isolates on brassica.
There was variation in aggressiveness between isolates for all brassicas as
measured by number of leaves wilted after 17 days (Fig.1 ) and lesion size.
S. sclerotiorum isolates from buttercup were generally less aggressive than
those from crop plants.
Turnip was the most susceptible brassica followed by oilseed rape and
broccoli.
Identifying Sclerotinia resistance
Two S. sclerotiorum isolates (high / low aggressiveness) were
used to screen a B. napus diversity set consisting of genetically
fixed lines representing a structured sampling of diversity across
the gene pool (www.oregin.info).
The diversity set exhibited a wide variation of responses to S.
sclerotiorum inoculation from highly susceptible to strongly
resistant (Fig. 2).
Further work is now confirming the response of potentially
resistant lines including inoculation tests at the flowering stage.
800
increasing resistance
increasing susceptibility
Resistance score
700
600
500
400
300
200
100
0
87 83 36 8 91 58 33 20 60 45 3 56 37 78 74 86 51 24 76 77 89 11 22 17 71 31 7 28 54 70 29 64 63 16 94 19 92 42 32 82 84 6 25 59 53 90 80 57 43 2 81 12 30 49 15 35 95 88 50 9 61 23 79 85 96 4 1 21 13 46 68 39 5 10 14 26 27 65 44 47 40 48 55 66 67 52 62 69 93 41 75 34 18 73 38 72
Accession number
Figure 2: Response of B. napus lines to S. sclerotiorum infection (aggressive isolate). Disease resistance score was based on degree of infection and number of leaves wilted.